When you’re planning out a deck—whether it’s your own DIY project or a major upgrade for a client as a contractor—the visible touches get all the glory. But those of us who’ve built and rebuilt enough decks (here in Saskatchewan, often in some very wild weather) understand just how important the "hidden details" are for a beautiful, lasting space. That’s especially true when it comes to what’s going on under your deck. A proper under-deck system isn’t just about keeping the area dry, it’s about protecting your investment, creating new opportunities for enjoyment, and future-proofing your outdoor haven.
At The Ultimate Deck Shop, we regularly help homeowners and pros compare under-deck systems. The big names on most Canadian projects right now are ZipUp UnderDeck, Trex RainEscape, and Dexerdry. Each has its own unique strengths and best-fit scenarios. This guide digs deep so you can make the right call—no pressure or salesy pitch, just our on-the-ground perspective after helping thousands of Canadian projects succeed.
How Do Under-Deck Systems Actually Work?
The core goal is simple: keep water from soaking your deck’s joists and framing, and channel it away to preserve both the structure and the space below. Ignoring drainage means rot, mold, and serious repair costs in the future. It’s also a lost opportunity for storage, shaded lounge areas, or even a "second outdoor room"—especially valuable in climates with unpredictable rain and freeze-thaw cycles.
- Above-joist systems: Installed on top of joists before deck boards are put down. These offer the most total protection and are preferred for new decks.
- Below-joist systems: Mounted under joists (beneath an existing deck), these are perfect for adding drainage and a more polished look to older or already-built structures.
Trex RainEscape: Comprehensive Protection for New Decks
Trex RainEscape is purpose-built as an above-joist waterproofing option. It stops water from reaching your deck’s frame by capturing and redirecting it at the top level.
- Material: Flexible, UV-resistant HDPE troughs and downspouts running between joists. Uses specialized butyl tape to seal seams.
- Protection: Stops water before it ever reaches structural timber, giving 100% substructure coverage.
- Warranty: Backed by a 25-year product warranty—something we always point out to those thinking long-term.
- Install Timing: Best for new construction, or total deck replacements (since it has to be installed before or during deck board placement).
- Amenities: Once installed, it enables reliable addition of lighting, ceiling fans, and even a finished dry room below the deck.
Trex RainEscape’s robust protection and warranty make it a favourite for new builds, particularly when clients want to maximize the lifespan of an advanced decking material. It’s also one of the more expensive up-front solutions, but when you compare it to the cost of replacing rotten joists, most see the investment as wise "insurance." For an installation overview and additional details, check our product overview.
Dexerdry: Smart Flange Waterproofing—Protection Without the Overhead
Think of Dexerdry as the low-profile but highly effective alternative. Rather than setting up troughs and downspouts, it uses a patented above-joist "flange" system. This creates a waterproof barrier at the exact point deck boards meet joists—where water is most likely to sneak in.
- Barrier at the Board: Dexerdry acts as a gasket between boards, stopping water from channeling between and down.
- Flexibility: Works with both wood and composite deck boards. Designed to allow natural movement, perfect for Canada’s freeze and thaw cycles.
- Economical: Lower in price than full above-joist drainage systems. The tradeoff: less of a "finished room" effect underneath, but robust substructure and joist protection.
- Best Use: Especially handy for board swaps or retrofits—you can generally install it without removing the entire deck.
For a deeper technical breakdown and fit options for your scenario, our Dexerdry deep-dive has more info: Dexerdry Profiles Explained: Create a Dry-Under-Deck Space Without Gutters.
ZipUp UnderDeck: Fast, Beautiful, and Retrofit-Friendly
ZipUp flips the logic: instead of intercepting water above the joist, it creates a ceiling below the joists. This offers both drainage and a super clean, finished look for the space under your deck. Key benefits from talking to hundreds of local customers:
- Retrofitting: No need to remove deck boards. Panels are attached underneath, so installation is quick and minimally intrusive—ideal for existing decks.
- Custom Finish: The system doubles as a beautiful finished ceiling, with various panel colours and trim rails to match your design.
- Flexible Panel System: Main rails, seam rails, and pitch rails let you adapt around posts, odd angles, and any architectural quirks.
- Water Control: While not quite as watertight as above-joist methods in extreme storms, ZipUp does a great job in typical scenarios. It quickly transforms a messy space into useable dry storage, a workshop, or a protected seating area.
- Maintenance: Panels can be unzipped for access if you ever need to run electrical or check framing—a huge bonus for future-proofing.
If you're curious how ZipUp integrates with deck builds or want to see its visual effect, our experts can demo sample pieces at our stores.
Product and Feature Comparison: At-a-Glance Table
| Feature | Trex RainEscape | Dexerdry | ZipUp UnderDeck |
|---|---|---|---|
| Installation Location | Above joists - requires open frame | Above joists (flange) or with board replacement | Below joists - can be retrofitted |
| Deck Board Removal Needed? | Yes, unless installed new | Only if replacing boards | No |
| Protection Level | Full substructure coverage | Critical board-to-joist protection | Good below-deck dryness |
| Creates Finished Ceiling | No (but you can add one) | No | Yes, included |
| Typical Project Fit | New builds/major renos | Existing decks, board swaps | Existing decks, fast upgrades |
| Supports Amenities Below (e.g., lights, fans) | Yes, directly compatible | Limited (only if extra steps taken) | Yes, with modification |
| Price Tier | Premium | Budget to Mid | Mid |
| Canadian Winters | Excellent freeze-thaw resistance | Designed for movement and weather | Performs well if slope is set correctly |
Choosing What’s Right for Your Project
- Building a brand-new deck, expect to stay for years, and want maximum peace of mind? Trex RainEscape is probably your match. It’s a bit more up front, but you get comprehensive substructure protection, an industry-leading warranty, and full support for under-deck amenities.
- Want to extend the life of an existing deck (without a huge reno), especially if you’re replacing boards? Dexerdry gives top-notch joist protection without the complexity of a full drainage system.
- Own an older deck, want a dry spot fast, or value a finished ceiling look? ZipUp UnderDeck is pretty tough to beat. Retrofit in a weekend, and your “under-zone” becomes a prime storage or hangout spot.
Critical Points for Canadian Homeowners and Contractors
- Seal every seam carefully. Even small gaps can let surprising amounts of water through, especially during a spring melt or fall downpour.
- Add at least a slight slope—about 1/8” per foot—so water actually runs out instead of pooling.
- Consider your project’s future needs. Planning ahead for under-deck wiring, lighting, or even future repairs is a small step that saves big headaches.
Still Debating Which Under-Deck System Fits?
Every property, climate, and budget is unique—and most of our customers appreciate the hands-on advice we’ve gained from years of Canadian deck projects. Want to know more about how your choice integrates with the decking material you’re planning, or if you need to replace boards before upgrading your drainage? We cover those issues and more in our blog, including guides like comparing the cost of composite decking in Canada and installation advice for Saskatoon homeowners.
If you want one-on-one help, our expert staff in Regina or Saskatoon can review your project and answer your toughest "What if?" scenarios. We’re happy to walk you through real product samples, so you can see and feel the difference between systems before you buy. Or just explore our full decking materials lineup for inspiration and further technical deep-dives.
Bottom line: an under-deck system is more than a nice-to-have, especially in our climate. Investing in the right solution keeps you dry, happy, and confident about your outdoor space—spring, summer, fall, or even those wild winter days that sometimes show up early. Let us help you build it right, from what’s under your feet to the finished look above.
